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Herschel Wedge heat build up in larger apertures


Space Hopper

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Hi guys,

As we have an eclipse coming up, i'd thought i'd dust off the Herschel wedge and have a practice run with some sun bothering. A beautiful day here in Derby with not a cloud in the sky.

 

It also gave me the chance to try out my new zoom eyepiece on the sun for the first time. It performed well, although i found using a lower power setting gave the more pleasing views.

There was nothing too exciting to see sunspot wise, with 'region 3124' showing close to the limb being the standout group.

 

IMG_4586

 

IMG_4587

 

Not long after i thought i may have some problems with the wedge / scope combo.

After a few minutes of viewing i thought that i could smell something getting overly hot, and sure enough

a finger on the wedge's heat window confirmed it. Not burning hot, but much hotter than i'd seen before

when using my last scope (105mm aperture) which only rendered it 'gently warm'.

I've read the recommended refractor size to use with the HW is 80mm - 120mm approx and anything much bigger 

can cause a heat build up.

This was the first time i'd used my 140mm scope for HW Solar, and i'd kind of taken warnings of using bigger apertures with a grain of salt. Now i know it's an issue, i'll only be having much shorter viewing and imaging runs and make sure the scope is pointed away from the sun at regular intervals to let the wedge cool a bit.

 

I also worry a bit about using an 'oiled triplet optic' for Solar viewing with a HW but TEC assure me this is fine.

 

 

IMG_4588

 

Heres a couple of images, just prime focus using a Canon EOS R and 2x Powermate (1960mm focal length)

iso 100,  1/320 sec.  Tweaked and cropped using MAC Photos.

Thanks for looking.

 

8547A5F0-4CE7-4C08-BC09-4399B7CB14F9_1_201_a

 

8547A5F0-4CE7-4C08-BC09-4399B7CB14F9_1_201_a

 

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I have used the Baader Herschel wedge with a 6” refractor on multiple occasions. I do remember the same smell the first time but it seemed to dissipate. I have left the scope pointing at the sun for several hours at a time when imaging but for visual I moved the scope away from the sun when not observing as per the instruction manual. Overall I have had no issues using the wedge with a 6” aperture scope. From the manual:
 

Maximum telescope size: We have used the Herschel prism succesfully with telescopes with 6 and 8 inch aper-
ture. Because of the huge amount radiation, we recommend to point the telescope away from the sun when you do not observe - make a break every hour or so to give the equipment time to cool down. The limiting factor for the focal length is the 2" adaption. The image of the sun in the image plane is ca. 1cm per 1m focal length, so focal length should not be longer than ca. 4,5m. If you can project the sun with your telescope and a 2"- focusser, you can also use the Herschel prism.

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Thanks for the reassurance ; thats good to know.

Theres actually a picture on the Baader HW box showing it set up on a German Zeiss 200mm refractor scope.

I definitely smelt something getting very hot earlier though, i wonder if there was some dust / debris inside that was starting to burn a bit ?

I always used the wedge before with a smaller sized refractor, most recently a 105mm / 650 short tube.

Although the heat window got a bit warm, even in the height of summer, it never got really hot like it threatened to today.

You can't be too careful though with the sun and in future i will observe in short intervals just to be on the safe side.

That is until i buy another smaller scope.......

 

 

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My wedge is cheap and fires the sun at a bit if aluminium foil that scatters the light out the side. Less safe for people nearby, but nothing to absorb heat. I’ve only gone upto 80mm, so do t know how it’s do with larger aperture. The ceramic should take significantly more temperature than other parts of the unit, your nose was a good sensor.

Peter

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I’m sure the smell was just a bit of dust burning off and nothing to worry about. If you think about it, it is heading into late October and the Sun is not that high or strong. People use wedges all over the world and in much hotter climes than here with no problems. I’ve used mine in a 130mm scope on a fairly hot day with no issues, so I’m sure it is fine. The benefit of a wedge (not to mention the image quality) is that they are fail safe. If it falls out of the scope you might just get a hot leg! In the very unlikely event the prism does crack then you will just get worse image quality/a dimmer image; there won’t be any danger to your eye.

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You could always stop the scope down with a thought given to a higher amount of energy collected by the larger objective and coming into the wedge there is also a higher amount of energy at the eyepiece (controllable with the polarising filter) in the same way there is a higher amount of heat being dissipated by the wedge. Binoviewers split this energy between two eyes which is another thought. 

As a side note. I never forgot the smell of my commodore VIC-20 (more than forty years ago?) when it got hot. Things do give of vapours when they heat up. 

Edited by StarryEyed
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I don’t want to take over this thread but as it’s a recent thread with lots of real life wedge users in I hope someone may help ..

Can anyone point me toward the relevant thread that compares the view between an apeture white light filter and the Herschel wedge for visual please ?? I found it before and now I cannot find it anywhere maybe I’ve just been looking at the sun too long lol 

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1 hour ago, Moon-Monkey said:

I don’t want to take over this thread but as it’s a recent thread with lots of real life wedge users in I hope someone may help ..

Can anyone point me toward the relevant thread that compares the view between an apeture white light filter and the Herschel wedge for visual please ?? I found it before and now I cannot find it anywhere maybe I’ve just been looking at the sun too long lol 

This one?

 

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I have used a HW on my 220mm refractor with no issues, visually only and I don't observe for protracted sessions.  Seeing conditions seldom support the aperture so I prefer something in the 100mm range.  The objective of a refractor is subject only to the ambient solar temperature, not the focused.      🙂

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+1 for dust in the wedge - I noticed my wedge smoking during a session a month ago, que big panic, but the wedge turned out to mildly warm on the outer surface of the heatsink - so I assumed there had just been a piece of debris - perhaps a seed or even an unfortunate insect, that had wafted into the wedge. I guess if something more substantial had entered the wedge it may have produced heat such as the OP describes.

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The 2" Lacerta wedge heat sink used to get hot after hours of tracking the sun with my 180mm/7" f/12.
Nothing to worry about though. The inside of the heat sink became discoloured after a while.
But then so did the outside of my 1.25" Lunt wedge. Which only received ambient sunshine.
The matt black finish eventually faded to brown. A suntan? :wink2:

 

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On 19/10/2022 at 07:47, StarryEyed said:

You could always stop the scope down with a thought given to a higher amount of energy collected by the larger objective and coming into the wedge there is also a higher amount of energy at the eyepiece (controllable with the polarising filter) in the same way there is a higher amount of heat being dissipated by the wedge. Binoviewers split this energy between two eyes which is another thought. 

As a side note. I never forgot the smell of my commodore VIC-20 (more than forty years ago?) when it got hot. Things do give of vapours when they heat up. 

The Vic was my first PC as well. 1982 or was it 81 ??

Followed by the C64 and an Amiga after.

Those were the days ! 😃

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9 minutes ago, Space Hopper said:

The Vic was my first PC as well. 1982 or was it 81 ??

Followed by the C64 and an Amiga after.

Those were the days ! 😃

Ha Ha, I was very similar, Vic 20, then C64 and then the Amstrad 128 and I made an extender card with more memory to give me a massive 256 Kb.

Steve 

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